The invention is related to delayed gelation systems that can be particularly used for water control processes in the oil industry.
This type of processing for some underground formations, crossed by injection or production bore holes, is well known in principle to those skilled in the art, as well as the difficult problems which it raises. It will be useless to discuss here these operations. This invention is concerned with selectivaly plugging an underground zone able to allow a water invasion into a producing layer.
It was first proposed, in the U.S. Pat. No. 3,614,985, using urea and aluminium chloride to cause a delayed aluminium hydroxyde precipitation.
The French patent application no. 85 10 272 applied July 2, 1985 proposed using aluminium hydroxychloride which allows accurately controlling the precipitation time, the structure and the morphology of the precipitate.
The French patent application no. 86 06434 applied Apr. 30, 1986 proposes using hexamethylenetetramine and the French patent application no. 86 14089 applied Oct. 8, 1986 recommends the adjunction of an adjuvant for the activator (sodium cyanate).
The teaching of all the above mentioned documents is incorporated here as a reference and those skilled in the art can refer to those.
The above discussed techniques have reached an efficiency and an accuracy which are satisfactory taking into account the extreme difficulty of the technical problem raised.
An object of the invention is to further improve some aspects of these techniques and to substantially reduce their cost which in between has become an absolutly determining parameter in the oil industry.
Namely, one of the major inconveniences of the water control techniques generally is their very high cost. This is caused by the necessity of using large volumes of fluid to obtain the desired effect. Namely, it is very often necessary to treat the permeable basin over several meters, possibly several tens of meters, depth and not only in the immediate surroundings of the bore hole.